It is well known that heat can be a problem in many environments, and that overheating can lead to failure of components such as integrated circuits (e.g. a central processing unit (CPU) of a computer) and other electronic components. Heat sinks are a common device used to prevent overheating. Heat sinks rely mainly on the dissipation of heat from the device using air. However, dissipating heat using a gas, such as air, is difficult because of the poor thermal properties of gases. Gases have low thermal conductivities, which inhibits heat absorption. They also have low heat capacity, which causes them to heat up quickly after absorbing only a small amount of heat. This retards the rate and the amount of heat absorption by decreasing the temperature difference between the gas and the heat sink.
Conventional heat sinks have a limited amount of surface area that can be put into a given volume. As a result, these heat sinks are large, especially in the direction perpendicular to the heat source and substrate. Additionally, these heat sink designs do not integrate well with certain types of fluid pump designs.
A novel heat sink described in U.S. patent application Ser. No. 11/181,106, filed Jul. 13, 2005, and entitled “Micro-Channel Heat Sink,” the contents of which are incorporated by reference herein, dramatically advances the state of the art of heat sinks. It describes a structure comprised of a large array of relatively short micro-channels that allows heat to be more readily transported through short, low thermal resistant paths. As a result, heat sinks based on this concept have a fraction of the volume of traditional heat sinks while maintaining high performance cooling.
The heat sink described in U.S. patent application Ser. No. 11/181,106 and other more conventional heat sink designs typically rely on fans and blowers to promote flow of gases through their structures. Meanwhile, other techniques have been developed that directly convert electricity into fluid flow. These methods are collectively referred to as electro-hydrodynamic (EHD) pumps. One of these methods of pumping a gas is called corona wind. It refers to the gas flow that is established between two electrodes, one sharp and the other blunt, when a high voltage is applied between the electrodes. The gas is partially ionized in the region of high electric field near the sharp electrode. The ions that are attracted to the more distant, blunt electrode collide with neutral molecules en route and create a pumping action.
Another type of EHD pump is described in U.S. patent application Ser. No. 11/271,092, entitled “Ion Generation by the Temporal Control of Gaseous Dielectric Breakdown,” filed on Nov. 10, 2005, the contents of which are incorporated herein by reference. In this method, ions are generated by a temporally controlled breakdown of the gas and are then attracted to oppositely charged electrodes to create a pumping action.
U.S. Patent Publication No. 2005/0007726 A1, entitled “Ion-Driven Air Flow Device and Method,” relates to an ion-driven, fluid flow generating microscale pump device and method for creating a flow of gaseous fluid for the purpose of cooling solid objects. The ion generation involves an electron tunneling process and the EHD pumping uses a traveling electric field concept. The concepts of this patent application are interesting but are impractical and complex in many respects.
U.S. Pat. No. 6,659,172, entitled “Electro-hydrodynamic heat exchanger” relates to a counter flow heat exchanger with EHD enhanced heat transfer. The flow is not primarily driven by an EHD pump, but rather an external device of some kind. The EHD action presumably creates secondary flows that enhance the heat transfer rate of the system and improve its performance.
U.S. Pat. No. 4,210,847, entitled “Electric wind generator” discloses a corona wind pump to provide air flow for heat transfer purposes. However, there is no mention of heat sink integration.
U.S. Pat. No. 4,380,720, entitled “Apparatus for producing a directed flow of a gaseous medium utilizing the electric wind principle” discloses a corona wind device for moving air. It includes an aerosol addition that enhances the electro-hydrodynamic coupling, i.e. it increases the efficiency of the pumping action.
U.S. Pat. No. 5,237,281 entitled “Ion drag air flow meter” and U.S. Pat. No. 4,953,407 entitled “Ion-drag flowmeter” disclose reverse corona wind devices that measure the ion current to determine the air flow velocity.
The above prior art teach concepts that are interesting, but applying them to effective heat sink structures remains a problem. It would be desirable to have a heat sink design with improved gas flow characteristics over that of a traditional fan or passive techniques, along with a structure that could support and effectively employ more advanced gaseous flow techniques.